Photoaffinity labeling has been employed to identify amino acids at the active sites of enzymes and in the controlled inactivation and isolation of enzymes and receptor proteins. Bifunctional protein reagents with photoreactive groups have also been used to map enzyme or membrane structure. The first goal of this project is to synthesize and characterize several new photoreactive bifunctional protein reagents. Each compound will have one inherently reactive group with specificity for a single nucleophilic amino acid residue, such as methionine or lysine. In addition, there will be a 14C-diazoester group which is inert but can be activated by UV light. The reactive groups will allow the photosensitive ones to be delivered to the individual Met or Lys residues of enzymes where one such residue has been shown to be essential for activity or especially reactive. Once anchored to the enzyme, the compound will be photolyzed to yield highly energetic carbenes which can insert into even the most inert nearby amino acids. These carbenes thus map the original residue to others near it in the folded protein structure in solution. A second goal is to extend photoaffinity labeling to the light stimulated inactivation of enzymes which are targets of conventional chemotherapy. Analogs of folic acid containing photoreactive azido and diazo functions will be prepared. These will be used in the attempted UV inactivation of dihydrofolate reductase and thymidylate synthetase. New "sulfa" drugs will also be synthesized which contain photosensitive azide moieties. These will be employed in attempting to inhibit bacterial folate synthesis and growth by means of long wavelength ultraviolet irradiation. The above compounds may be important in treating skin disease and infection.